Community Forums

wingtip · 12-05-2018, 01:12 PM

We are getting ready to head south soon and have been putting our new solar/battery/inverter setup through its paces. We have 740 amp/hrs of Trojan L16 AGM batteries and a 2800 watt Magnum Inverter. Wire runs between Batteries and Inverter are short, less than 3 feet and we have a small 4 cup 600 watt coffee pot. Noticed that during the brew process of about 5 minutes the voltage dropped to 12.25 and then immediately bounced back up to 12.87 as soon as the brewing stopped. Voltage was below 12.3 for about three minutes. State of charge stayed around 99%. This is the highest draw item we have (normally boil water for our drip when boondocking). Will this kind of temporary high load damage our batteries?

babock · 12-05-2018, 01:21 PM

Not at all.

nothermark · 12-05-2018, 01:26 PM

Did you try looking up the specifications for your batteries?

For 600 watts you would draw ~5 Amps at 120 VAC. That roughly translates to 50 Amps @ 12VDC with efficiency losses. Divide that by the number of 12 V battery strings and see what Trojan says about current draw.

RoadDogYVR · 12-05-2018, 01:35 PM

Trojan's website gives a 75 amp draw capacity minute figure of 215 minutes for that battery so a 50 amp draw is safe.

drdarrin · 12-05-2018, 06:14 PM

We regularly use our inverter to power the microwave. According to my meter, it draws between 150-175 DC amps for up to 5 minutes. Batteries are still going strong after 3 years of use.

twinboat · 12-05-2018, 08:13 PM

Your not hurting the batteries with that draw.

If your reading the volts at the inverter, I'm wondering what size cables you have between the inverter and batteries.

Take a reading right at the batteries to see how much voltage drop your getting thru the cables.

rarebear.nm · 12-05-2018, 08:24 PM

As others have said- no that draw is safe. It is normal to see a voltage drop that bounces back.

Do you have a battery monitor, like a Trimetric 2030 by Bogart? That will read voltage at the batteries if installed correctly.

wingtip · 12-05-2018, 11:14 PM

Thank you everyone for your input.

We have a Victron battery monitor. I've forgotten the actual cable size (1/0?) but it's big, maybe the diameter of my thumb. We know not to draw our batteries down below 50% and normally keep the limit much higher than that.

What spooked us was the low voltage alarm (on the Victron). We had it set at 12.3 volts and it activated part way through the brewing experiment at about the 2 minute mark, although the little coffee pot didn't skip a beat. All this got us thinking about high amp draws and the effect on our batteries.

We didn't set our system up to brew coffee or to cook in the microwave specifically but to provide us with sufficient power to live (frugally) and run essential systems while boondocking. We have a whole-house setup and other than the coffee pot and micro I can't think of anything else that would draw this much (A/C is wired for gen or shore only) just want to make sure we don't subject our investment to abuse.

bluepill · 12-05-2018, 11:23 PM

FWIW, I set my low voltage alarm for 11.8 volts. That means it will trip under a 50 amp DC load when the batteries are actually at about 12.3 volts under no load. That's about 60% state of charge. Eliminates false alarms.

Loren Rice · 12-05-2018, 11:34 PM

I believe occasional hard draws are actually good for a lead acid battery. Your coffee pot time and rate is fine and occasional micro wave use, maybe limited to a few minutes. Don't think id do a 2hr run (no turkey baking) What's bad is to draw a battery bank down to 10.5 which is considered dead. Don't want to do that. Drawing a battery bank down to no lower than 80% is a good way to keep your batteries around for a long time.
Next thing is to have a good three stage charger. a charger that when your batteries are charged will go into a maintenance level of 13v. at that voltage you don't boil the water out but still maintain the charge perfectly. These often now days are in better inverters/ chargers. But sometimes in older less expensive rigs you'll find a converter/charger that are pretty brutal on batteries. I've heard people exclaim my batteries were good when I got here two months ago and now their dead. That's because their charge portion of the inverter maintained the batteries at too high a voltage. Again when on standby 13v. is the sweet spot.

Hope this helps, There's a lot more to be said but I tried to hit the hi spots .

rarebear.nm · 12-05-2018, 11:50 PM

Our low voltage alarm is set for 12.0 volts. I wired a bypass switch in so if the alarm has disengaged the power I can bypass it for some vital function, but knowing what I'm doing at the same time.

Our solar system has provided 100% of the 12 volt recharge for almost a year now. The breaker switch to the converters has been off all that time. Even under heavy furnace use I don't see battery charge dropping under about 92% in the morning. We have 460AHs of battery capacity.

**Spdracr39** · 12-06-2018, 06:58 AM

If you are concerned get a battery temp sensor. Its the heat that damages them not the current draw. ( disclaimer this does not include extreme circumstances or running the voltages down under 12 v when not under load).

twinboat · 12-06-2018, 07:57 AM

The 20 hour discharge rate is 5 amps per 100 AH capacity.

With 740 AH that's a bit over 35 amps. Do that for 10 hours straight and you will use 50% of your capacity.

At the 10 hour rate, you can draw 74 amps for a bit less then 5 hours, before you've used 50 % of the AH in the battery bank.

If you look at the Trojan Specs, you will see a 5 and 1 hour discharge rate. The fact that they list them, strongly suggest that you can discharge them at that rate.

Even the RC lists 75 amps as a discharge rate for RC minutes.

wingtip · 12-07-2018, 10:24 AM

Both our Magnum inverter/charger and Morningstar solar controller are fully programmable for our AGM batteries and are temperature compensated so we're getting a pretty good picture of what's going on.

It's cold here (-6ºC) and we accidently overloaded our system yesterday morning (three aux heaters, furnace, coffee pot and microwave ... oops).
Circuit protection on the Magnum shut it down while the batteries gave us time to turn stuff off. Voltage dipped to 11.9 briefly and came right back up while SOC stayed above 95%. Had to reset the Magnum and clear an error on the Morningstar but otherwise all was good.

Still trying to get a working handle on battery temp as it relates to charging voltage. I'm guessing the sensors will make adjustments to charge voltage automatically ... I'm back into the books on that subject this morning.

We're also adjusting alarm settings on the Victron and we'll see how that goes towards reducing false alarms.

Slowly getting educated on this new system and we're pretty happy with it so far! Looking forward to Quartzsite in January and seeing how it performs in a warmer climate. Appreciate all the tips and advice!